Fusion Drives desperately need to be standard, but otherwise this is a nice Mac.

The back of the iMac. It really does look exactly like the non-Retina models.

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Nearly the same ports: Headphones, SD card, four USB 3.0, two Thunderbolt 2, and gigabit Ethernet.

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The fan vent tucked away under the stand.

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The new Magic Keyboard picks up a layout a lot like the 2015 MacBook's.

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The new keyboard's angle is shallower than the old one's.

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A comparison.

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Underside.

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On/off switch, Lightning port, antenna cutout.

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The two Magic Mice. You can't tell the difference between them, but the new one is on the left and the old one is on the right.

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The differences become more apparent on the other side.

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The Lightning port, used for pairing and charging.

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The Magic Trackpad 2 (right) is larger than the original and adds Force Touch.

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The new trackpad's angle is shallower than the old one's.

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The undersides are mostly similar.

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On/off switch, Lightning port, antenna cutout.

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It's been over three years since the very first Mac went Retina, and we're still waiting for every model to get the upgrade. But this year, the scales started to tip in Retina's favor. We got an all-new Retina MacBook in the spring, and today Apple is killing the 27-inch non-Retina iMac and introducing a new 4K model at the top of the 21.5-inch lineup.

The 4K iMac starts at $1,499 and does for the 21-inch iMac what the 5K version did for the 27-inch iMac a year ago: it gives it a Retina screen and leaves pretty much everything else alone. You do get a handful of nice internal upgrades, including Intel's Broadwell CPUs and GPUs, Thunderbolt 2 support, and faster storage and RAM (all also available on the refreshed non-Retina 21.5-inch iMacs). But for most intents and purposes, this thing is just a 2012-era iMac chassis with a nice sharp screen installed in place of the old 1080p display.

Today we're looking at the base model of the 4K iMac, the cheapest configuration you can buy if you want that Retina screen. In the coming weeks, we'll be able to take a closer look at the higher-end 27-inch models.

Look and feel

The 4K iMac's design is the same as the one Apple introduced back in 2012, the last time it redesigned the iMacs. Compared to the iMac body used from roughly 2009 to 2011, it's lighter and it's thinner all the way around the edges. A metal stand that protrudes from the back of the computer lets you tilt the screen up and down but not from left to right, and all of the computer's ports—a headphone jack, SD card slot, four USB 3.0 ports, two Thunderbolt 2 ports, and a gigabit Ethernet jack—are all on the back where they stay out of sight. This can be irritating to use if you're just trying to plug in a USB stick.

In short, if you've seen an iMac in the last three years, you've seen this one too. There are just a couple of things to be aware of if you're stepping up from an older 2009, 2010, or 2011 model: the new single-fan setup keeps the iMac cooler and quieter than those older models, all of which could get worryingly hot under load. The integrated speakers in the 21.5-inch versions of the post-2012 design are also subtly weaker and tinnier, though the 27-inch versions sound fine. And, of course, the optical drive is long-gone.

The biggest change between this iMac and one purchased in 2012, screen aside, is the new lineup of accessories Apple is shipping alongside it. We've got more extended impressions of the new Magic Keyboard, Magic Mouse 2, and Magic Trackpad 2 here, but the short version is that all three peripherals are logical sequels without many surprises. The new keyboard has stiffer keys and a layout identical to the Retina MacBook's. The new Magic Trackpad gets a Force Touch upgrade and is clickable from edge to edge. And the new Magic Mouse glides over the surface of your desk or mousepad more easily (but otherwise looks pretty much the same).

All three accessories get new rechargeable li-ion batteries that are rechargeable via (included) Lightning cables, and those Lightning cables are also used to pair the accessories to new Macs. Another nice touch is that the cables will carry data if you connect them to your Mac, removing the need for separate wired peripherals. When you buy a new iMac you get a Magic Keyboard and a Magic Mouse 2, with the option to switch to a Magic Trackpad 2 for an extra $50.

New screen

Further Reading

The new 4K iMac has a display resolution of 4096×2304, which by default can show the same amount of information as a 2048×1152 non-Retina screen. Using OS X's Retina scaling, you can switch into 2304×1296 and 2560×1440 display modes. So if you want, you can use this 21.5-inch iMac to show the same amount of information as a 27-inch iMac, a nice added benefit to using a Retina screen.

The resolution is an odd choice. Usually, Retina versions of existing computers quadruple the resolution of the existing non-Retina version. The 5120×2880 screen on the 5K iMac, for example, has four times the pixels of the standard 2560×1440 iMac, and the 2880×1800 display on the 15-inch Retina MacBook Pro has four times the pixels of the standard 1440×900 MacBook Pro. By that logic, a 21.5-inch version of the Retina iMac should have a 3840×2160 screen, but Apple has chosen to tweak the display so that both of the Retina iMacs share the same 217 PPI pixel density.

Because of this slightly-higher-than-standard resolution, Apple is still using the custom timing controller from the 5K iMac to drive the display at its full resolution at 60Hz. The 4K iMac can drive a single 3840×2160 screen over a DisplayPort 1.2 cable, but it can't drive a second display at the same resolution as the internal display; that will need to wait for DisplayPort 1.3. Presumably for the same reason, the 4K iMac doesn't support Target Display Mode, since no current Mac could drive it at its native resolution at 60Hz over a single cable.

Another addition that comes to both the 4K and 5K iMacs is a wider color gamut—previous iMacs used the sRGB color space, but the new Retina models support "over 99 percent" of the DCI-P3 color space common in digital movie theaters. DCI-P3 encompasses the entire sRGB color space but is capable of displaying more shades of red and green (which also affects secondary and tertiary colors like yellow, orange, magenta, and cyan, though blues in DCI-P3 are roughly the same as in sRGB).

To support this wider color gamut, Apple has switched away from using standard white LEDs for backlighting, which typically combine a blue LED with a yellow phosphor to create white. Apple is now using red-green phosphor LEDs to expand the color gamut, a strategy previously demonstrated by LCD makers like Sharp.

We've gone through the non-Retina-to-Retina transition a few times now, so you know how it goes: the new screen is pretty and sharp and even if you don't particularly care what color space it supports you'll appreciate how colors pop, particularly bright ones like the orange Ars logo. The level of detail is often useful, especially when you're looking at image thumbnails, and the ability to scale the display to make the 21-inch iMac show the same amount onscreen at once as the 27-inch iMac is genuinely useful.

But as with the 5K iMac, I come away with the impression that Retina just isn't as essential on a desktop as it is for other devices, at least not for most people. More detail and support for higher resolutions via screen scaling is great when your face is a foot or two away from your laptop, but I sit a bit farther away from my desktop and I just don't notice the extra detail as often. The screen is great, it's just less obviously useful here than it is elsewhere in the iOS and OS X lineup.

Andrew Cunningham
Andrew has a B.A. in Classics from Kenyon College and has over five years of experience in IT. His work has appeared on Charge Shot!!! and AnandTech, and he records a weekly book podcast called Overdue. Twitter@AndrewWrites